Pulse width modulation (PWM) systems are used to generate analog signals from digital data. PWM signals can be used to drive an H-bridge or similar device (such as an amplifier or other buffer circuit) to achieve high power and high efficiency amplification. An ideal H-bridge is simply a buffer that reproduces the digital waveforms with higher output amplitude. Preferably, the buffer has a fixed delay, providing edge transitions (rising or falling) at its output at a fixed time offset from the input.
Unfortunately, the propagation delay of a practical H-bridge implementation may be variable and/or signal dependent. In Class D amplifiers, such as those used in audio applications, propagation delay variations through an H-bridge or buffer circuit represents a non-linearity. Such a non-linearity can result in degraded Total Harmonic Distortion of the audio signal. If spectral energy spreading techniques have been applied to the PWM signal, such a non-linearity can cause high frequency noise to fold into the lower frequencies of the audio band or the band of interest, resulting in harmonic distortion or degraded signal-to-noise ratio (SNR).